A common practice in the preparation of a shower or tub bath, is to open the hot water valve to purge the cold water in the line coming from a water heater. In this manner, a volume of water approximately equal to the volume contained in that line is wasted as it flows out into a drain. Furthermore, as the hot water valve is shut at the end of the bath, the hot water remaining in said line begins to cool, often losing most of the sensible heat it had originally gained in the water heater.
In an attempt to avoid the waste of water, users sometimes place a container, such as a pail, to collect the purged water for some appropriate later use instead of letting it go down the drain. Besides the chore involved in doing this, the waste of heat is not eliminated.
U.S. Pat. No. 4,372,372 discloses a shower bath economizer to effect an energy saving by transferring heat from the spent shower bath water to the cold water supplied to the shower bath closet. To this end, it is provided a heat exchanger in the outlet line of the spent water leaving the shower bath closet, through which the incoming cold inlet water is directed, thereby raising its temperature prior to entry into the shower bath closet. Although the water heater needs to supply less hot water, there is still an initial volume of cold water existing in the pipeline between the water heater and the shower bath closet wasted as it flows out into the drain.
U.S. Pat. No. 8,656,526 discloses a recirculating shower system to recycle part of the used water in a shower. The system is provided with a heater for heating the recycled water to a temperature at which microorganisms are killed, and a heat exchanger arranged to exchange heat between the water flowing towards and away from the heater, thereby reducing the heating load on the heater. A hydrocyclone is needed to separate the used water into a clean water portion and a waste water portion. The clean water portion is returned directly back into the circuit for recirculation, whereas the waste water portion is directed to a waste water pipe.